Sodium batteries with graphene protection promise faster charging and up to 10,000 cycles

Sodium-ion batteries are becoming an increasingly attractive alternative to lithium-ion batteries, as they are based on more affordable and widely available raw materials, offer greater safety, and work well even at low temperatures. However, manufacturers have until now had to choose between two options: enable ultra-fast charging or ensure a long battery cell life. Fast charging breaks down the structure of the nanosheets, which shortens their lifespan compared to established LFP technology.

A research team from China may have found a way to overcome this trade-off. They have developed an anode made of titanium dioxide nanosheets, about 10 nanometers in size, that form hollow double-shell spheres. The key innovation is a graphene coating, just 0.4 nanometers thick, that surrounds each individual nanosheet. Simply mixing graphene with other materials did not yield the same results, while a direct protective layer increased electrical conductivity.

The test results are very promising. At a fast charge rate of 10C, which theoretically takes about six minutes, the anode maintained a capacity of 131 mAh/g even after 10,000 cycles. At a rate of 100C, when charging would take about 36 seconds, it reached a capacity of 121 mAh/g. In comparison, the unprotected nanosheets collapsed after about 400 cycles. The larger sodium ions put a heavy load on the anode surface during the rapid charge, and the graphene protective layer prevents the formation of cracks and excessive reactions with the electrolyte.

All of these measurements were, of course, performed under laboratory conditions. In addition, the anode operates at a higher average voltage than conventional hard carbon anodes, which can reduce the overall energy density of the entire battery. Of course, the new technology will need to be validated in larger, commercially designed battery cells and packs before it can be used in mass-produced electric vehicles.